1. Field of the Invention
The present invention relates to measuring features and conditions of boreholes of wellbores in the oil and gas industry. More particularly, the present invention relates to a system for taking measurement of a diameter of the borehole after drilling and underreaming the borehole. The present invention also relates to a system for taking measurement of a diameter of the borehole simultaneous with drilling and underreaming the borehole. Additionally, the present invention relates to a method of verifying the diameter of a borehole during and after drilling and underreaming.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Drilling is part of a process for extracting a natural resource, such as ground water, natural gas, and petroleum, or for exploring the nature of the material underground. A well or borehole can be created by use of a drilling rig to rotate a drill string, which has a drill bit attached at its end in order to bore into the ground to a desired depth. Drill collars and drill pipe sections add length, weight and support along the drill string as the borehole deepens, and different types of drill bits cut into all types of rock formations and soil combinations. Drilling fluid or drilling mud pumps through the inside of the string, out of the drill bit by nozzles or jets, and up the annulus to the surface, in order to create the proper physical and hydrostatic conditions to safely drill the well. Additionally, the rock cuttings are removed from the borehole in the drilling mud circulation flowing to the surface.
After drilling a section of hole, steel casings, which are slightly smaller in diameter than the borehole diameter, are placed in the hole. Cement can be injected in the annular space between the outside of the casings and the borehole. The casing system strengthens the integrity of the new section of the borehole to allow for deeper drilling and other benefits. A series of smaller and smaller drill bits with corresponding smaller steel casing systems are used for drilling, such that a completed well includes holes within holes. In the prior art technology, the diameter of the borehole decreases as each section of the casing systems are put in place.
However, the latest developments in drilling require deeper and deeper wells, even super deep wells from holes five to six miles below the surface. The continuing reliance upon fossil fuels, in particular oil and gas, has pushed the drilling and exploration industry to explore ultra deep waters (water depths more than 2000 m) with super deep wells drilled to depths over more than 7500 m. The temperature, distance, and pressure conditions of super deep wells require a vast amount of resources to extract oil and gas. The newly extreme depths cannot be reached with the prior art technology because the decreasing size of the diameter of the borehole set a limit on the depth of drilling.
The industry response to form super deep boreholes has been reaming or under-reaming, which enlarges the diameter of the borehole by removing a layer of the already stressed and disturbed material caused by the drill bit. Reaming has been known in metalworking and machining to affect mechanical properties for a good surface finish. Applied in the field of wellbore drilling, an underreamer is an activated cutting tool on the drill string to enlarge the borehole. The typical underreamer has a set of retractable and extendible parallel straight or helical cutting edges along the length of a cylindrical body and is placed higher than the drill bit along the drill string. The cutting edges have an angle and with a slight undercut below the cutting edges for making initial contact with the sides of the borehole.
The adaptation of underreamers has lead to even greater challenges in the oil and gas industry. Controlling the drill bit and the drill string in the borehole has always required special attention. Measurement While Drilling (MWD) and Logging While Drilling (LWD) systems collect real-time data, which is data viewed while drilling, and memory stored data, which is data viewed after the bit run. The data helps to ensure the proper direction and conditions of the drilling and record formation properties. MWD systems measure and record readings, such as natural gamma ray, borehole pressure, temperature, resistivity, formation density, etc., and the data can be transmitted as fast as real-time via mud pulser telemetry, wired drill pipe or other means. Stabilizers added on the drill string are mechanical solutions to reduce drill string vibrations, improve directional hole accuracy, and improve drilling efficiency. At the newly extreme distances and depths achieved with reamers, it becomes even more important for accurate monitoring because of the costs and resources invested, and it has become even more challenging with the underreamer positioned in the drill string. The underreamer is a separate cutting tool, so the drilling diameter of the drill bit and the larger final diameter, after the underreamer, are different. The prior art does not provide for the final confirmation of borehole diameter, after the underreamer and while drilling.
For measuring the borehole diameter, the present typical system is a wireline mechanical caliper tool, which collects a caliper log of the tracked measurements of the size and shape of a borehole, after drilling the hole section has been completed and after the drill string and drill bit have been removed from the well. The borehole diameter is an extremely vital piece of information for super deep wells because the borehole must be a particular size in order to fit the proper casing system. The extreme depths required cannot be achieved, if the boreholes become too small for the casings. The extending stacking of the casings cannot be supported or selected correctly if the borehole dimensions are too small. The wireline mechanical caliper tool verifies the borehole diameter as it is opened and withdrawn from the bottom of the hole; two or more articulated arms push against the walls of the borehole, taking hole diameter measurements. This prior art wireline mechanical caliper tool requires complete stoppage of the drilling operation and withdrawal of all drilling equipment from the borehole. As such, the wireline mechanical caliper tool and the method of using the caliper tool are very significant in terms of rig time and efficiency for the well.
In the past, various patents have been issued in the field of borehole diameter measurement. For example, U.S. Pat. No. 7,168,507, issued to Downton on Jan. 30, 2007, and published as 20030209365, discloses an invention to recalibrate downhole sensors. A first set of inexpensive and small sensors are located in the drill string adjacent to the bit, and a second set of more accurate sensors is located in a more protected location higher in the drill string away from the drill bit. As drilling progresses, the second set collects data to calibrate an offset of the first set of sensors. The invention discloses the placements of sensors away from the drill bit for better accuracy to measure for gas influx into the borehole.
U.S. Pat. No. 5,200,705, issued to Clark, et al. on Apr. 6, 1993, teaches a system for determining a dip characteristic of formations surrounding a borehole and a method of using a transducer array having longitudinally spaced transducers. The electrodes are located on the stabilizer blades to detect electric current from the coil antennas on a drill collar above the stabilizers. The electrodes on the stabilizer blades function as a sensor for electric current.
U.S. Pat. No. 5,130,950, issued to Orban, et al. on Jul. 14, 1992, describes an ultrasonic measurement apparatus. This patent is one of several similar patents relating to measuring characteristics in boreholes. The '950 patent clearly discloses the placement of a sensor in a stabilizer, even though no reamer is shown. FIG. 1 shows a stabilizer 27 with a sensor 45. This prior art only measures the pilot hole.
United States Patent Application Publication No. 20080110253, published by Stephenson, et al. on May 15, 2008, discloses an invention for downhole measurement of substances in formations while drilling. The method includes waiting for substance that is dissolved in the drilling fluid to be in equilibrium with any of the substance in the earth formation cuttings and measuring the substance dissolved in the drilling fluid downhole. FIG. 1 shows a sensor 99 placed away from the drill bit 15 and above the stabilizer 140.
U.S. Pat. No. 7,434,631, issued to Krueger, et al. on Oct. 14, 2008, teaches an apparatus and method of controlling motion and vibration of an NMR sensor in a drilling BHA. The sensor is disposed in the drilling assembly for making a measurement of a formation parameter of interest. A non-rotating stabilizer is disposed in the drilling assembly proximate the sensor. The non-rotating stabilizer is adapted to reduce motion of the sensor below a predetermined level during the measurement. This invention embodies the prior art with the sensor locked in a single non-rotating position on the drill string, so the errors in readings occur.
UK Patent Application, GB 2460096, published on Nov. 18, 2009, by Wajid, discloses an underreamer and caliper tool having means for determining bore diameter. In this publication, the tool integrates the enlargement of the borehole and measurement of the borehole diameter. The tool body attaches to the drill string and has expansion elements housing the caliper. The expansion elements are the cutting tool after the drill bit, and sensors measure borehole diameter during or after the underreaming. The specialized expansion elements with real-time data allow for control of the underreaming process.
At present, there is no LWD (Logging While Drilling) equipment available, that is dedicated to measurement during drilling and underreaming, i.e. MWD (Measurement While Drilling) systems, to determine the final well-bore diameter of any hole section that has been drilled. Many companies claim to be able to provide ‘Real Time Well-Bore Diameter Measurements’, but in reality, such data is apparently an ‘inferred’ reading, or a ‘pseudo’ caliper reading, such that the accuracy is questionable. The problem seems to be associated with a number of factors: the changing composition of the drilling mud affects the reading, the borehole is irregularly shaped, and the position of the bottom hole assembly and the sensors are not usually equidistant to the borehole wall, such that the reading depends upon the position of the sensor.
It is an object of the present invention to provide a system and method for measuring features and conditions of a borehole. Diameter of a borehole is one such condition of the borehole to be measured by the present invention. Other features and conditions of MWD tools may be adapted into the system and method of the present invention.
It is an object of the present invention to provide a system and method for verification of a borehole. In particular, the system measures the “final” diameter of a borehole, which is a borehole after drilling and after underreaming.
It is an object of the present invention to provide a system and method for verification of a borehole during drilling and underreaming in real time. In particular, the system measures the real time “final” diameter of a borehole, which is a borehole during drilling and underreaming.
It is another object of the present invention to eliminate the need for separate caliper measurements of the final borehole.
It is still another object of the present invention to provide a system and method for verification of a final borehole compatible with existing technology.
It is an object of the present invention to provide a system and method for verification of a final borehole for any drilling and/or expansion operation of a wellbore.
It is another object of the present invention to provide a system and method for verification of a borehole with calibration means. In particular, the calibration means includes both a downhole and surface system for calibration of the sensor readings.
It is a further object of the present invention to provide a system and method for verification of a borehole before and after underreaming.
It is an object of the present invention to provide a system and method for verification of a borehole with improved accuracy of final borehole measurements.
It is another object of the present invention to provide a system and method for verification of a borehole to monitor the efficiency of the underreamer.
It is another object of the present invention to provide a system and method for verification of a borehole, which stabilizes the drill string while measuring the final borehole diameter.
It is still another object of the present invention to provide a system and method for verification of a final borehole in a cost effective and efficient manner.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.